This invention relates to an exhaust arrangement for outboard motors and more particularly to an improved arrangement for treating the exhaust gases in an outboard motor.
As is well known, an outboard motor consists substantially of a self contained power plant that can be attached to the hull of a watercraft for propelling it through a body of water. As a result, the outboard motor includes a prime mover, normally an internal combustion engine, a propulsion device and a transmission for driving the propulsion device.
Generally, the engine is positioned in the power head at the top of the drive shaft housing and is supported so that its output shaft rotates about a vertically extending axis. This permits coupling of the engine output shaft to a drive shaft that depends into the drive shaft housing and which drives a propulsion device in a lower unit through a transmission. Frequently, these transmissions are capable of shifting between forward and reverse conditions.
The outboard motor also includes a supporting arrangement between the coupling to the watercraft hull and the propulsion unit so that the propulsion unit can be steered generally about a vertically extending axis and to achieve tilt and trim movement generally about a horizontal axis.
Furthermore, the outboard motor must include an arrangement for facilitating cooling of the engine, induction of air charge to the engine and discharge of the exhaust gases to the atmosphere including a silencing arrangement. This latter function is one that provides substantial problems.
That is, in many applications for engines other than in marine applications, there is substantial space available for the exhaust system. The exhaust system for any engine should generally permit efficient flow of the exhaust gases to the atmosphere and also provide silencing and cooling of the exhaust gases so as to be relatively unobjectionable in noise and effect on the atmospheric conditions.
With an outboard motor, the space available for this exhaust treatment is relatively limited. Generally, outboard motors include in the engine some form of internal exhaust manifold through which the exhaust gases are passed from the combustion chamber to the exhaust system of the outboard motor. Generally, the exhaust system includes an expansion chamber that is formed in the drive shaft housing and an exhaust pipe arrangement for delivering the exhaust gases from the engine manifold to the expansion chamber.
The expansion chamber then discharges the exhaust gases to the atmosphere, generally through an under water high speed exhaust gas discharge. This is done so as to utilize the body of water in which the watercraft is operating as a silencing medium. Under low speed conditions, however, the under water exhaust discharge is relatively deeply submerged and the back pressure on the exhaust gases will not permit them to exit from this path. Therefore, there is normally provided an additional, above the water exhaust gas discharge which functions under this running condition.
The problem with these type of constructions is that the formation of the expansion chamber and various conduits that lead to the atmosphere become complicated and require a number of castings and other components that must be fitted together and assembled.
It is, therefore, a principle object of this invention to provide an improved outboard motor exhaust system wherein the exhaust path to the atmosphere can be simply and conveniently formed with a minimum number of separate components.
It is a further object of this invention to provide an improved exhaust manifold and an exhaust system for an outboard motor wherein the exhaust path is formed a minimum number of parts and wherein the number of interconnecting joints is substantially reduced.
As has been previously noted, it is also necessary to employ some form of system for cooling the engine of the outboard motor. Because of the fact that the outboard motor operates in a body of water, it is common to employ water cooling for the engine. This involves drawing water from the body of water in which the watercraft is operating, circulating it through the engine cooling system and discharging it back to the body of water in which the watercraft is operating. In this way, the body of water acts as the heat exchanger for the engine cooling system.
Although this arrangement is quite simple, providing the necessary flow path can be difficult. Furthermore and in accordance with another object of this invention, there is provided a path for the cooling water so that it can also assist in cooling the exhaust gases.
As has also been noted, it is the normal practice to mount the outboard motor on the transom so that it can be steered about a generally vertically extending axis and tilted and trimmed about a horizontally extending axis. Frequently, this results in somewhat complicated mountings arrangement.
It is a further object of this invention to provide an improved mounting arrangement for the steering movement of an outboard motor and wherein the mounting arrangement may function in combination with the exhaust system so as to further augment the available volume for an expansion chamber.